For a multiplicity of biological studies, it is necessary to isolate individual cells or structures from a cell ensemble, for instance tissue or a histological tissue preparation. This may for example be done with mechanical microtools, for example microcapillaries or microneedles. Such a procedure is laborious, however, and there is a contamination risk for the objects being isolated. Furthermore, such a method is scarcely automatable.
WO 97/29355 A in the name of the Applicant has therefore proposed a novel method for sorting and extracting individual biological objects, which are arranged on a planar carrier. In particular, it proposes separating a selected biological object from the surrounding other biological material by a laser beam, so as to prepare the selected biological object to be free from its surroundings. The biological object prepared to be free in this way is subsequently transferred in a catapult fashion from the carrier to a collection device with the aid of a laser shot, this collection device being for example a collection substrate. For example, a polymer film may be used as the carrier of the biological material.
A biological object to be separated from a biological material applied on the carrier is thus first selected, then cut out from the biological material and subsequently catapulted to the collection device by a laser-induced transport process. In the scope of the present application, “biological objects” are above all intended to mean living or fixed biological cells or cell components which are part of a liquid or solid biological substance, for example cell tissue, a smear, a cell culture or the like.
With the aid of the method described above particular objects can be deliberately detached or sorted from a biological material. The biological objects may be applied next to one another on a fixed planar carrier, and the process of extraction or sorting can be carried out within a short time and contactlessly. The survivability and the morphology of the biological objects are preserved, i.e. the biological objects are not damaged or harmed by the separation process and the laser-induced transport process.
The method described above, however, is to be carried out manually and is therefore relatively elaborate. High precision is furthermore necessary, since a biological object to be separated must be positioned precisely with respect to the laser beam in order to achieve reliable cutting and subsequent catapulting by a laser pulse or laser shot. Furthermore, in general similar cutting processes or catapulting processes must be carried out repeatedly with high accuracy.
For this reason, WO 01/73398 A in the name of the Applicant proposes to carry out the cutting and/or catapulting of the object with computer assistance. It proposes that a laser light source, which generates the laser beam used for the cutting and/or catapulting, should be controlled automatically and the relative movement between the laser beam and the carrier comprising the biological object, which is required for the cutting and/or catapulting, should be induced and controlled automatically. In particular, a plurality of cutting and/or catapulting processes can be carried out successively with computer assistance, i.e. automatically. This can ensure a uniform high precision for each individual cutting/catapulting process.
According to this method, the objects to be cut out or catapulted are selected by means of a user interface of a computer system. To this end a video image of the biological or nonbiological material is generated and overlaid with the user interface of the computer system. Manual selection of a multiplicity of objects by the user, however, entails considerable time expenditure. The manual selection of objects furthermore involves a risk that the selection will not be made according to objective criteria.